docs: def mpi(value):
      """Serialize multipresicion integer using GPG format."""
      bits = value.bit_length()
      data_size = (bits + 7) // 8
      data_bytes = bytearray(data_size)
      for i in range(data_size):
          data_bytes[i] = value & 0xFF
          value = value >> 8
  
      data_bytes.reverse()
      return struct.pack('>H', bits) + bytes(data_bytes)